[thelist] Networking: Localhost AND the net?

[Judah McAuley]

At 04:26 PM 12/8/00 -0500, you wrote:
>Thank you! I honestly didn't know what information to offer. I thank you 
>all for you patience with me. Networking is the one topic is still find 
>myself blindingly ignorant about.

No problem. Networking is an arcane art (at best).  It is all quite 
rational, and completely un-intuitive for the average user.

>>  IP address of all three machines (Are they static or
>>  dhcp?) Does your modem have a single IP address bound to
>>  it? If so, is the Mac doing network address translation?
>
>Mac1:     24.43.66.191   Mask: 255.255.255.128 (with Softrouter)
>Mac2:     192.168.232.2  Mask: 255.255.255.0
>PC:       192.168.232.4  Mask: 255.255.255.0
>
>Ethernet Adapter Info
>----------------------
>The PCI Fast Ethernet Adapter
>Adapter Address: 00-48-54-3A-32-4F
>IP Address: 192.168.232.4
>Subnet Mask: 255.255.255.0
>Default Gateway: 192.168.232.1

OK.  There is a bunch of stuff going on here.  First off, notice that Mac 2 
and PC have address in the 192.168.*.* range.  These are reserved addresses 
for unattached networks.  This means that these addresses will not be 
broadcast out to the general Internet, only to local machines.  In this 
case the router needs to be performing Network Address Translation 
(NAT).  Essentially, this maps external "real" IP addresses (like 
24.42.66.191) to "fake" IP addresses (like 192.168.232.4 and 
192.168.232.2).  When a request goes out, the NAT daemon creates a 
temporary mapping between the internal (fake) IP address and the IP address 
of the external connection.  It sends the request along to the external 
requested address using one of the "real" IP addresses it is allocated, and 
when the external host responds, it passes the response back to the machine 
with the internal IP address that made the request.  This allows one "real" 
IP address to be used by several machines with "fake" IP 
addresses.  Traffic that originates from the external world bound for an 
internal machine gets more complicated, but since it doesn't bear on this 
question, we will leave it for another time.

What this means practically, is that any NAT daemon/router needs to have at 
least 2 IP addresses, an internal and an external.  I don't know exactly 
how Softrouter works, so you might want to poke around and see what the 
internal IP address is, since you are currently reporting the external IP 
address.

One potential problem is the Default Gateway setting on your PC.  The 
Default Gateway is the same thing as your Router (in this case, 
Mac1).  What happens is that when you make an IP request, the machine looks 
at the Subnet Mask.  The Subnet Mask determines what addresses are local 
and what addresses exist on the other side of a gateway.  With a subnet 
mask of 255.255.255.0 and an IP address of 192.168.232.4, this means that 
all of 192.168.232.* (where * is 1 to 254) is considered local.  A request 
in that range will scan the local network, but will not pass the request 
along to the gateway.  If the request is outside of that IP address range, 
then the request is passed along to the gateway address.  It could be the 
case that your router (Mac1) is not listening on the 192.168.232.1 
address.  If it's not listening on that address, then the traffic outside 
your local network will never get out.

Unfortunately, I don't remember how to get the gateway information from 
Open Transport, since I haven't done much Mac suportt for several 
years.  But if you can find the gateway (or it might be labeled 'router') 
information on the Internet connected Mac2, then make sure that it's the 
same info as on the PC.  If not, then change the gateway on the PC in the 
properties of TCP/IP in the Network control panel.

>>  Also, try running a Traceroute our from the PC so we can
>>  see what the machine is trying to do. From the command
>>  prompt run "tracert www.yahoo.com"
>
>DOS Box pops up. Hub lights for the PC flashes, I get a little bit of send 
>from the cable modem, Mac1 and Mac2 flash on the hub I can't detect a 
>pattern. A results appears, but only one line, and the DOS box disappears 
>before I have a chance to read it.  (How do I make the DOS box stay, and 
>not disappear after showing results for more than one second?)

You have to open the DOS prompt before you type in the command.  Go to 
Start ->Programs->MS-DOS Prompt
Then type "tracert www.yahoo.com"
This will keep the window open.

>Does this help at all? Is there any other relevant info I've missed?
>
>Thanks!

It does help.  Try the traceroute and also check for the internal IP 
address within Softroute and check the gateway setting on Mac2 and make 
sure that the PC setting matches.  Then post the resulting info and we'll 
try to figure it all out.

Judah